Put the peppers in a medium roasting tray (or an ovenproof frying pan will do) and splash with 2 tbsp of the oil. Season generously, then roast with the chicken at 200C/fan 180C/gas 6 for about 20 mins, until softened a little. Sit the bunches of tomatoes among the peppers, scatter the cumin over everything, then drizzle with the rest of the oil.
Season again, then roast for about 10 mins until the tomato skins have split. Toss the olives through just before serving. Can be made up to a day ahead and served cold, or reheated in a hot oven for 5 mins.